And to relaunch his international commercial career by taking on senior board roles in Australia and further afield.
This segue is more difficult if a politician has been branded a loser as former Australian Prime Minister John Howard found out when he outstayed his welcome.
But Key leaves National in the lurch without an election game plan that does not rely on "Brand Key" to pump up its overall party support. And this is without obviously developing younger contenders to ensure a generational change at the top.
In eight years in office he has run a tight ship.
His kitchen cabinet - English, Gerry Brownlee, Steven Joyce, Murray McCully and latterly Paula Bennett - has been stable.
But given his CEO-style leadership of Cabinet, eight years is a long time to run with the same senior executive team.
Frankly, if Key had thought it time for a shakeup for his own position, he could have applied the logic more widely.
Key has provided huge reassurance to New Zealand during a difficult period. He leaves a more confident country in his wake.
He has positioned New Zealand well on the international stage as his predecessor Helen Clark generously said in a tweet on Monday.
But the economic boom-times have left the country facing a major infrastructure catch-up. Many New Zealanders are now priced out of the Auckland housing market. There are pockets of misery that have yet to be addressed.
They have not been addressed on the Key/English watch.
English, for all his fine qualities as finance minister, has been positioned by Key as the fait accompli option.
I've previously written that if Key "fell under the proverbial bus" then English would be the obvious politician to step into the top job and provide stability.
He may, in all likelihood, still be the obvious politician when National MPs vote in their new leader next Monday.
It has become a commonplace to suggest that Steven Joyce will automatically step into the finance role if English is elected leader.
But leaving the Key kitchen cabinet in charge would be short-sighted.
If English wins what yesterday afternoon turned into a three-horse race he will have the opportunity to form his own kitchen cabinet and signal a generational change.
Joyce will have enough on his plate strategising for the 2017 election. And judging by the results in the Northland and Mt Roskill by-elections there won't be much time for taking on a new Cabinet role.
He is at his best promoting business and fronting the country's economic growth strategy.
The finance minister role requires a politician of strong discipline: Coleman could fit that bill perfectly.
Which leaves what to do with Collins. The Oravida fracas makes it unlikely she could easily be shoehorned into the foreign affairs role assuming McCully also steps down as expected next year.
But she is a strong player and is needed back on the front bench.
New Zealand has good reason to be grateful to Key for the way he (and English) managed through the global financial crisis (remember the "rolling maul" of policies?); the earthquakes and Pike River.
National MPs who have ceaselessly prefaced their verbal communications with "John Key" to build credibility with their audiences can finally develop a brain and think for themselves.
It will be a different environment minus "Brand Key". National will have to work that much harder to address underlying issues and that is a good thing.
